A system-in-package (SIP), also known as a chip stack, generally includes a number of integrated circuits packaged in a single module. In the SIPs, dies containing integrated circuits may be stacked vertically on a substrate, such as another die or a wafer. Unlike electrical connections within an integrated circuit stack, which are formed during fabrication of the integrated circuits themselves, the dies do not have pre-existing electrical connections to the substrate and such electrical connections between the die and the substrate are established after the dies are formed and during fabrication of the SIPs.
Various methodologies may be employed to electrical connect the dies to the substrate in the SIPs. For example, wire bonding or flip chip technology may be employed to electrically connect the dies to the substrate. With wire bonding, a bond pad that is electrically connected to die is connected to a bond pad on the substrate through a fine off-chip wire. Wire bonding generally offers excellent design flexibility, with a wide range of possibilities for bond pad locations while still enabling connection through the wire.
Flip chip technology, also known as controlled collapse chip connection, enables electrical connection of the die to the substrate through solder bumps that have been formed on the die. The solder bumps are formed on a top side of the die and, in order to mount the chip to external circuitry on the substrate (e.g., a circuit board on another die or wafer), it is flipped over so that its top side faces down, and aligned so that the solder bumps align with matching pads on the substrate. The solder is then reflowed to complete the interconnect. This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry. Flip chip technology offers more efficient electrical connection between the die and the substrate than wire bonding, with the possibility for simultaneously forming numerous electrical interconnects between the die and the substrate. However, design flexibility is compromised with flip chip technology due to the need to have the solder bumps and corresponding bond pads in alignment. However, wire bonding and flip chip technology are generally incompatible due to the uniform nature of solder bump formation across all bond pads on the die when flip chip technology is employed.
Accordingly, it is desirable to provide articles including bonded metal structures and methods of forming the same in a manner that enables efficient electrical connection between the metal structures while also enabling design flexibility. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.